The present invention relates to a method for producing an outer skin for an electric deposition foil producing drum used for producing metallic foils such as copper foil, ferric foil and stainless steel foil through the electric deposition.
An electric deposition foil producing drum of such a type is known from Japanese patent Examined Publication No. 58-24507, Japanese Patent Examined Publication Nos. 61-60149 and 62-233, and Japanese Patent Unexamined Publication No. Hei 2-243790.
FIGS. 1 to 3 show a typical example of an electric deposition foil producing apparatus. An outer skin 2 made of titanium in the form of a cylinder is shrink-fitted to an outer circumferential surface of an inner drum 1 made of carbon steel or the like to thereby form an electric deposition drum a. A shaft b of the deposition drum a is rotatably supported by bearings c and d. A rotational power source is connected to the shaft b. A lower part of the deposition drum a is dipped into an electrolyte liquid f of an elecctrolyte bath e. An anode g is disposed in the electrolyte bath e. Using the electric deposition drum a as a cathode, an electric supply is effected between the electric deposition drum a and the anode g through a ring h and the shaft b. An electric current flows through a path from the outer skin 2 to the inner drum 1 through a fit interface i, and during a period when the electric deposition drum a is being dipped into the electrolyte liquid f upon the rotation thereof, a metallic foil that is a deposition material j is deposited on the outer circumferential surface of the outer skin 2. The metallic foil is peeled away from the outer circumferential surface of the deposition drum a. Thus, the coutinuous production is possible.
The outer skin 2 is made by winding a planar material of titanium in the form of a cylinder and welding opposite edges of the planar material through a TIG welding or a plasma welding. This is finished by the cutting and grinding processes.
However, the prior art plate-splicing welding portion 3 of the outer skin 2 is left without any treatment. This plate-splicing welding portion 3 of the outer skin 2 of pure titanium shown in FIG. 4 was observed (anywhere the surface was mirror-ground and erroded and its metallic formation was photographed). As a result, it was found that there was a significant contrast among a base material portion A', a thermally affected portion B' and a welded portion C'. This was due to the fact that, whereas the base material portion A' had a smooth surface, the thermally affected portion B' and the welded portion C' had the rough surfaces.
On the scale of 100 times, it was observed that the base material portion A' was shown in a microscopic picture of FIG. 5, the thermally affected portion b' was shown in a microscopic picture of FIG. 6 and the welded portion C' was shown in a microscopic picture of FIG. 7. It was found that the surface formation of the base material portion A' was an isoaxial d crystal as a rolled annealed formation, the surface formation of the thermally affected portion B' was a rough planar d crystal and the surface formation of the welded portion C' was a sawtoothed d crystal. The reason for this is that the base material portion A' was a uniformly intimate or fine formation, whereas the thermally affected portion B' and the welded portion C' are a deformed rough formation due to the thermal effects of the welding operation.
For this reason, the electric deposited metallic foil produced by the electric deposition foil producing drum using the outer skin 2 was a corrugated rough one at the plate splicing welded portion. There was a fear that it was impossible to use it as the printed circuit board due to a cut or short-circuit. This would lead to the reduction of yield as well as the difficulty in producing the continuous foil.
In order to solve this problem, the above-described Japanese Patent Unexamined Publication No. Hei 2-243790 discloses the method for producing a titanium outer skin for the electric deposition foil producing drum. However, the plate splicing welding thereof is attained by a method in which an inverted V-shaped opening portion opens toward the outside of the spliced portion of the outer skin and wherein the welding is effected from the outside of the outer skin.